[Python-ideas] __iter__ implies __contains__?

[Oleg Broytman]

On Mon, Oct 03, 2011 at 06:31:08AM +1100, Steven D'Aprano wrote:
> Devin Jeanpierre wrote:
> >>Since iteration over elements is at the heart of containment tests, the same
> >>reasoning applies to __contains__.
> >
> >I was with you for the old-style sequence iteration API, but you've
> >lost me here. I *can* imagine use-cases where "in" shouldn't work:
> >pretty much any iterator. Doesn't it seem strange that `x in A` should
> >succeed, but then `x in A` should fail?
> 
> No. That is implied by the iterator protocol

   This is exactly the issue that is being discussed. In my very humble
opinion classes that produce non-restartable iterators should not allow
containment tests to use iterators.

Oleg.
-- 
     Oleg Broytman            http://phdru.name/            phd at phdru.name
           Programmers don't die, they just GOSUB without RETURN.